1. Field of the Invention
The present invention relates to a semiconductor device that is thin and lightweight, and a method for manufacturing the same.
2. Description of the Related Art
In recent yeas, cellular phones spread with progress of communication technology. Furthermore, more moving images and more information are greatly expected to be sent in the future. On the other hand, personal computers for mobile are produced by virtue of the weight saving. A large number of portable information terminal such as PDA (personal digital assistants), which begin from an electronic notebook, are produced, and are being widely used. Moreover, most of such portable information devices are each equipped with a flat panel display with the development in display devices.
In such a display device, brightness in the periphery of the display device is detected, and its display brightness is adjusted. Thus, needless electric power  consumption can be eliminated by detecting brightness in the periphery and obtaining moderate display brightness. For example, such an optical sensor device for brightness control is used for cellular phones and personal computers (for example, Reference 1: Japanese Patent Laid Open No. 2003-60744).
As a material of an optical sensor, a semiconductor is mainly used, and silicon is given as a representative example of the semiconductor material. As optical sensors using silicon, there are an optical sensor using single crystal silicon or polysilicon and an optical sensor using amorphous silicon. As for the optical sensor using single crystal silicon or polysilicon, sensitivity is highest in the infrared region of approximately 800 nm, and has sensitivity even at approximately 1100 nm. Therefore, in the case of sensing white fluorescent light that hardly include a spectrum of the infrared region and sunlight having a wide spectrum from the ultraviolet region to the infrared region, there is a problem that sensing results of each light are different while actual illuminance thereof are equal.
Further, the optical sensor using single crystal silicon is used as a resin sealing package using a lead frame for mounting on a wiring board or the like, or a package in which a single crystal silicon is mounted on a resin substrate provided with a circuit pattern by a wire bonding method or a face down method.
On the other hand, the optical sensor using amorphous silicon hardly has sensitivity against light in the infrared region, and has the highest sensitivity in a range of about 500 nm to 600 nm that is a center of wavelength of the visible light region. That is, the optical sensor using amorphous silicon has sensing characteristics that are similar to human visibility. Therefore, the optical sensor using amorphous silicon is preferable.
On the other hand, a light-transmitting plastic substrate is preferably used instead of a glass substrate. This is because a plastic substrate is thinner and lighter than a glass substrate, and a wiring board mounting them and electronic devices using it can be also thinner and smaller. Further, this is because a plastic substrate is flexible and can be set on a curved surface. Moreover, an element that can resist an impact can be provided by using a plastic substrate having flexibility.
However, since a plastic substrate is thin, a connection terminal cannot be formed on a side face of a substrate. Therefore, a connection terminal is formed on one surface of the substrate so as to a wiring board. A wiring board and an optical sensor are fixed by only one surface with a solder, and its area for bonding is small. Thus, there is a problem that mounting strength is weak as compared with a side electrode structure since the bonding area is small.
In addition, it is difficult to see a connection portion of an electrode of the optical sensor and an electrode terminal and to judge whether these connects to each other surely, because a region where the wiring board is connected to the optical sensor is in the lower part of a substrate of the optical sensor.
In addition, since some conventional organic resin materials or plastic substrates have poor heat-resistance, they cannot be mounted on a wiring board by a reflow step using solders.
Further, the optical sensor using single crystal silicon has a packaging structure, in which a wiring region for mounting an optical sensor (for example, regions provided with a lead frame and a circuit pattern) is larger than an area for functioning as an optical sensor. Accordingly, such a packaging structure of an optical sensor is interfering with high integration on a wiring board.